The present invention relates to an imaging lens unit, and more particularly, to an imaging lens unit installed in a compact imaging device. The invention further relates to an imaging device and portable terminal.
The demand for smaller imaging lens units has increased as imaging devices have become more compact. Imaging devices are now often installed in portable terminals. Thus, and increasingly low profiles and greater compactness in the optical axis direction are sought to conform to the thickness of portable terminals. Although reduction in the number of lenses forming an imaging lens unit is effective for achieving a lower profile, optical characteristics would become inadequate since proper aberration correction is difficult in configurations of just one or two lenses. There is thus a demand for technology which can provide a lower profile without adversely affecting the optical characteristics. For example, Japanese Laid-Open Patent Publication Nos. 2006-154767 and 2006-301403 disclose imaging lens units that have tri-lens configurations which use meniscus-shaped lenses for the first and second lenses as viewed from the object side.
In order to correct aberration with a limited number of lenses, each lens configuring the imaging lens unit desirably uses an aspherical lens that is unlikely to produce aberration. An aspherical lens is difficult to manufacture when using glass and is thus manufactured by injection molding normal plastic. To ensure the required strength, there are restrictions on the lens thickness when performing injection molding. Thus, extremely thin plastic lenses cannot be manufactured.
However, there are growing demands for low profile imaging devices which can be installed in increasingly thinner portable terminals. Although each lens in an imaging lens unit must be further reduced in size to cope with these demands and realize even lower profiles using the art techniques described in the above publications, there are limits to manufacturing thinner plastic lenses as described above.